Iontophoretic system for transdermal delivery of active agents for therapeutic and medicinal purposes

ABSTRACT

An embodiment of a system includes a power source and at least two electrode assembles. The power source that an output current that alternates between a maximum current value and a minimum current value; a pair of electrode assemblies. Each electrode assembly is configured to be held in contact with a skin layer of a user. Additionally, each electrode assembly includes an electrode that is coupled to the power source to receive the output current from the power source. At least one of the electrode assemblies in the pair includes a medium that carries an active agent having a charge, the medium being provided on the at least one electrode assembly to enable the output current to repel the active agent into the skin layer for a duration in which the output current has a polarity that is the same as a polarity of the active agent.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.13/481,466, filed May 25, 2012, entitled “Iontophoretic System forTransdermal Delivery of Active Agents for Therapeutic and MedicinalPurposes”, which is a Continuation of U.S. application Ser. No.12/537,243, filed Aug. 6, 2009 and Issued as U.S. Pat. No. 8,190,252 onMay 29, 2012, entitled “Iontophoretic System for Transdermal Delivery ofActive Agents for Therapeutic and Medicinal Purposes”, which claims thebenefit of priority to Provisional U.S. Patent Application No.61/152,251, entitled “Kit, System and Method for TransdermalIontophoretic Delivery of Therapeutic Agents”, filed Feb. 12, 2009; allof the aforementioned priority applications being hereby incorporated byreference in their respective entirety for all purposes.

FIELD OF THE INVENTION

Embodiments described herein relate to iontophoretic transdermaldelivery of active agents for therapeutic purposes.

BACKGROUND

Iontophoresis is a non-invasive method of propelling high concentrationsof a charged substance, known as the active agent, transdermally byrepulsive electromotive force using a small electrical charge. Thismethod has been used for the transdermal delivery of various compoundsincluding therapeutic agents. Traditionally, direct current has beenused to provide the driving current for iontophoresis. However there area number of short comings associated with the use of direct currentincluding limitations on the total amount of current that can bedelivered over time without causing injury to the skin, as well as thebuild up of capacitive charge in the skin layer which can oppose theelectromotive driving forces thus reducing the rate and total amount ofcompound delivered over time. Also direct current can cause a localanesthetic effect to the skin resulting in burns and other thermaldamage to the skin because the user doesn't feel the injury to the skinoccurring at the time. Thus there is need for improved methods fordelivering various therapeutic agents using transdermal iontophoresis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an iontophoretic system for transdermal delivery ofan active agent, according to one or more embodiments.

FIG. 2 illustrates an alternative embodiment in which each of a pair ofelectrode assemblies are equipped to disperse an active agent into theskin layer, under another embodiment.

FIG. 3 is a top view of the electrode assemblies deployed on a skinlayer of the user.

FIG. 4 illustrates an alternating power source for use with embodimentssuch as described with FIG. 1 though FIG. 3.

FIG. 5A through FIG. 5F illustrate various waveforms or current outputvariations that can be used to promote a characteristic of the electrodeassemblies operation on a user's skin.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments described herein provide for an iontophoretic system fortransdermal delivery of drugs and other therapeutic agents. As usedherein, the term transdermal refers to the delivery of a compound, suchas a drug or other biological agent, through one or more layers of theskin (e.g., epidermis, dermis, etc). Iontophoresis is a non-invasivemethod of propelling high concentrations of a charged substance, knownas the active agent, transdermally using electrical current applied atthe skin layer. The active agent can include a drug or other therapeuticagent or biological compound.

More specifically, embodiments described herein include a system fortransdermal delivery of active agents for therapeutic and medicinalpurposes. The system includes a power source and at least two electrodeassembles. The power source provides an output current that alternatesbetween a maximum current value and a minimum current value; a pair ofelectrode assemblies. Each electrode assembly is configured to be heldin contact with a skin layer of a user. Additionally, each electrodeassembly includes an electrode that is coupled to the power source toreceive the output current from the power source. At least one of theelectrode assemblies in the pair includes a medium that carries anactive agent having a charge, the medium being provided on the at leastone electrode assembly to enable the output current to repel the activeagent into the skin layer for a duration in which the output current hasa polarity that is the same as a polarity of the active agent.

According to one or more embodiments, an output current such asdescribed is a charged balanced alternating current (AC) output. Thecharged balance AC output means over a given duration, the amount ofcurrent delivered at each polarity is substantially equivalent. As usedherein substantially equivalent means that two values are within 80% ofone another, and more preferably within 90% or 99% over the period ofone or more waveforms.

Single Point Disbursement

FIG. 1 illustrates an iontophoretic system for transdermal delivery ofan active agent, according to one or more embodiments. A system 100 isshown in a deployed (i.e. operational) state, and comprises a pair ofactive electrode assemblies 110, 112 and alternating power source 108that combine to enable the transdermal delivery of a medicinal ortherapeutic (“active”) agent 102 into a user's tissue. Therapeutic agent102 can comprise one or more drugs or other therapeutic agents. In thedeployed state, the pair of electrode assemblies 110, 112 are positionedon the exterior skin layer of the user. In one embodiment, thealternating power source 108 forces the agent 102 to be dispensed fromone of the electrode assemblies in the pair (shown as electrode assembly110 in FIG. 1). More specifically, the active agent 102 is selected tohave an ionic charge, and the alternating power source 108 is connectedto electrode assembly 110 to repel the active agent 102 into the skinlayer of the user at instances when the alternating power source has thesame polarity as the active agent. As such, the driving mechanism thatcauses the active agent 102 to dispense into the skin layer isintermittent and alternating (to match the output of the power source108).

With specific reference to FIG. 1, the power source 108, electrodeassemblies 110, 112 and user skin layer or tissue form a circuit toenable delivery of the active agent from at least one of the electrodeassemblies. More specifically, FIG. 1 illustrates a single disbursementconfiguration in which the first electrode assembly 110 contains theactive agent, and the second electrode assembly 112 serves as a returnwithout the active agent. In the configuration shown, the secondelectrode assembly 112 serves as the return for completing the circuitwith power source 108 and the first electrode assembly 110. For aduration, the output current is provided a polarity that matches that ofthe charge of the active agent. The presence of the output current,flowing via the circuit formed by the other electrode assembly and thepower source 108, results in the charged active agent being repulsedfrom the electrode assembly 110 into the skin layer of the user. Thus,in a configuration shown by FIG. 1, the first active electrode assembly110 is equipped with the active agent 102, and the power source 108directs the active agent from the first electrode assembly 110 into theskin layer when the polarity of the output current matches that of thecharge of the active agent.

As described below, the power source 108 may vary the output of thecurrent output to alternate durations in which the active agent isdelivered. In one embodiment, the power source 108 varies the outputcurrent between a maximum current value (coinciding with a deliveryduration) and a minimum current value (coinciding with non-deliveryduration). The minimum current value corresponds to either no currentoutput, or a reverse current output. As described elsewhere, the reversecurrent output may serve as a retention mechanism that activelyprecludes the active agent from diffusing into the skin layer (e.g., dueto electrostatic attractive forces). Thus, a delivery duration coincideswith a duration in which an output current from the power source 108 haspolarity to match that of the active agent. A non-delivery durationcoincides with either an output current from the power source that isopposite in polarity to that of the active agent, or to a duration thatcoincides with substantially no current output.

In a system such as described with FIG. 1, some embodiments provide forthe delivery/non-delivery durations to be symmetrical or equal. Forexample, delivery/non-delivery durations may each last x milliseconds,seconds, or minutes, to match, for example, symmetrical waveforms of theoutput (e.g. sinusoidal, square wave etc.). In other embodiments, thedelivery/non-delivery durations are asymmetrical or unequal. Forexample, the delivery duration may last several minutes, and thenon-delivery duration may last only seconds or otherwise be less thanthe delivery duration. The delivery/non-delivery durations may repeat,or pass through only a single cycle (i.e., one delivery duration and onenon-delivery duration).

Each electrode assembly 110, 112 includes an electrode 130 and a contactthickness 118. The contact thickness 118 of each electrode assembly 110,120 may be in form of a patch fabricated from layers of elastomeric orother flexible polymer material. The contact thickness 118 may include,for example, adhesives for enabling the respective electrode assemblies110, 112 to be deployed on the skin layer of the user and to remainadhered over an extended period of time during movement of the skin.Likewise, the electrode 130 corresponds to one or more elements orlayers that extend the conductive path from the alternating power sourceto the contact thickness and/or skin layer. In one embodiment, aconnector 132 connects the electrode 130 to leads 133 of powers source108. The electrode 130 corresponds to a metal layer or element(s) (e.g.wiring, contact elements etc.) that extends or connects to the connector132. The electrode 130 may comprise a separate layer from the contactthickness 118, which includes a medium 122 for carrying the active agent102. However, in some variations, the electrode 130 includes elements,such as particles or contact elements, that are integrated or providedwith the contact thickness 118. In one implementation, the electrode 130is comprised of conductive material, such as metal (e.g. silver) orconductive carbon material (graphite sheets). In an embodiment depictedby FIG. 1, electrode 130 is a conductive layer that overlay the contactthickness 118. As described below, the contact thickness 118 includesthicknesses for dispersing the active agent 102, as well as material toenable the electrode assembly to be adhered to skin. In manyembodiments, the active agent is dissolved in an aqueous or othercarrier solution, for example, isopropyl alcohol, DMSO and likecompounds.

As previously mentioned, in an embodiment of FIG. 1, only one of theelectrode assemblies in the pair (shown as electrode assembly 110) isused to deliver the active agent 102 into the user's skin. The medium122 of the first electrode assembly 110 provides a reservoir or retainerthat contains the active agent, for example, in embodiments where theactive agent is dissolved in a carrier solution. More specifically, themedium 122 of the contact thickness 118 includes a tissue contactingporous layer 124, which can either be separate or part of a reservoir.The porous layer 124 can be configured to absorb the carrier solutionfrom the reservoir and in turn wick the solution into contact with theskin (e.g. by capillary action). The porosity of the porous layer 124may be selected based on various parameters. For example, the porositymay be selected based on the concentration or transport characteristicsof the active agent. More specifically, for example, high porosities canbe selected for higher molecular weight therapeutic agents and/ortherapeutic agents solutions having greater viscosity. Suitable porousmaterials for porous layer 124 can comprise compressed cotton or otherfibrous meshe such as meshs made from various polymer fibers

The electrode assemblies 110, 112 can be constructed as disposable orreusable. If disposable, the electrode assembly 110 (carrying the activeagent) is manufactured or retailed to include the active agent in themedium 122. If reusable, an embodiment provides that the electrodeassembly 110 includes an intake conduit and optional self-sealing portthat enables the active agent 102 to be dispersed in the medium 122 fordelivery. In one embodiment, the self-sealing port is formed fromsilicone or other elastomeric material, so as to enable the electrodeassembly 110 to be filled with the active agent.

The alternating power source 108 may correspond to a battery, such as arechargeable Lithium-Ion battery pack. As an alternative, thealternating power source 108 may, include or provide an interface, toanother power source, such as a solar cell. Circuitry (such as describedwith FIG. 4) may be used to convert the direct-current (DC) power outputto an alternating signal of a specified waveform. As mentionedelsewhere, the specified waveform may be short (e.g. milliseconds), long(minutes), symmetrical (delivery/non-delivery are equal), orasymmetrical (delivery/non-delivery are now equal).

The electrode assemblies 110, 112 and the alternating power source 108may be provided in connection with one or more housing segments. Forexample, the power source 108, electrode assemblies 110, 112, and wiringor connectors that interconnect the power source and the electrodeassemblies may all be contained by a housing, or combination ofintegrated housing segments. In this way, the system of electrodeassemblies 110, 112 may be provided as a product, device or kit that canbe assembled and deployed by the user. The kit may further includeinstructions for use.

When deployed and made operational, the active agent is selected to havean ionic charge that can be sufficiently repulsed by the presence ofcurrent having the same polarity. The active agent is distributed in themedium 122 of the electrode assembly 110. The power source 108 isconnected and signaled, resulting in a circuit being formed between thealternating power source 108, electrode assembly 110 containing theactive agent, and the electrode assembly 112 providing the returnelectrode. In the durations when the current has the same polarity asthe charge of the active agent, the active agent is repulsed from themedium 122 of the electrode assembly 110 into the skin layer of theuser. In the durations when the current has the opposite polarity as thecharge of the active agent, the active agent is not repulsed. Thus, theactive agent is induced to travel into the skin layer in alternatingdurations to match the alternating power of the alternating power source108. The frequency of the alternating power source 108 may vary greatly.In particular, the frequency of the alternating power source may be inthe range of milliseconds (e.g. 1/60 seconds) or minutes (e.g. tenminutes).

Among other benefits, the diffusion of the active agent into the skinlayer can be completely stopped with the switch in the current polarity.Thus, use of the alternating power source 108 enables the active agentto be stopped from entering the skin layer at alternating instances.This enables, for example, better control of the amount of active agentdelivered into the skin layer in a given duration.

Double Point Disbursement

FIG. 2 illustrates an alternative embodiment in which each of a pair ofelectrode assemblies are equipped to disperse an active agent into theskin layer, under another embodiment. More specifically, an embodimentof FIG. 2 shows a first and second electrode assembly 210, 212, each ofwhich can include a construction similar to that shown with the firstelectrode assembly 110 of FIG. 1. Accordingly, the first and secondelectrode assemblies 210, 212 each include an electrode 230 positionedover or in operative relationship to a contact thickness 218. Thecontact thickness 218 of each electrode assembly 210, 220 may be in formof a patch fabricated from layers of elastomeric or other flexiblepolymer material. The contact thickness 218 may include, for example,adhesives for enabling the respective electrode assemblies 210, 212 tobe deployed on the skin layer of the user. Likewise, the electrode 230of each electrode assembly 210, 212 may correspond to one or more metallayer or element(s) (e.g. wiring, contact elements etc.) that extends orconnects to a connector 232, which in turn connects that electrode 230to leads 233 of powers source 208. On each electrode assembly 210, 212,the electrode 230 may comprise a separate layer from the contactthickness 218, which includes a medium 222 for carrying the active agent202. However, in some variations, the electrode 230 includes elements,such as particles or contact elements, that are integrated or providedwith the contact thickness 218. In one implementation, the electrode 230is comprised of conductive material, such as metal (e.g., silver orsilver-silverchloride) or conductive carbon material (e.g., graphitesheets).

The medium 222 of the electrode assemblies 210, 212 includes a tissuecontacting porous layer 224, which can either be separate or part of areservoir. Similarly, in an implementation in which one or both of theelectrode assemblies 210, 212 reusable, a self sealing port (not shown)may be included to enable the active agent to be dispersed in the medium222 for delivery to the skin layer.

As a variation, the electrode assemblies 210, 212 may both be capable ofretaining the active agent to dispense, but the electrode assemblies210, 212 may have differing constructions. For example, the contactlayer and amount of active agent 202 each electrode assembly 210, 212can retain may be different.

In contrast to an embodiment of FIG. 1, the alternating source 208 iselectrically connected to cause dispersion of active agent 202 from bothelectrode assemblies 210, 212 in alternating fashion. In one embodiment,the alternating power source 208 alternates the power signal to eachelectrode so that the delivery durations form each electrode assemblyare the same. Such a configuration enables delivery durations toalternate between electrode assemblies. Among other benefits,alternating the delivery durations between electrode assemblies enablescontinuous transdermal delivery of active agents using alternatingpoints in the user's skin, to avoid, for example, skin irritation orsaturation.

Similar to prior embodiments of FIG. 1, an embodiment such as describedwith FIG. 2 may be constructed as a device or kit that can be assembledand deployed for use by the user. Accordingly, one or more housingsegments may be incorporated to integrate the electrode assemblies 210,212 and/or power source 208.

FIG. 3 is a top view of the electrode assemblies deployed on a skinlayer of the user. The electrode assemblies 310, 312 may be implementedto disperse an active agent from one electrode assembly (single pointdisbursement, such as described with FIG. 1) or from both electrodeassemblies 310, 312 (double point disbursement, such as described withFIG. 2). In a single point disbursement configuration, the alternatingpower source 308 repulses the active agent into the skin 322 (into thepaper, as depicted by Z axis) in alternating durations when the suppliedcurrent has the same polarity as the charge of the active agent. Asmentioned elsewhere, the alternating durations may last milliseconds,seconds, or minutes. The alternating durations may also be asymmetricalor unequal in duration. In a single point disbursement, for example,current is extended from the alternating power source 308 through thecontact thickness (see element 118 of FIG. 1) of the first electrodeassembly 310, into the skin layer 322, and to the second electrode 312(serving as the return) to form a circuit with the alternating powersource 308. The active agent is thus dispensed from one electrodeassembly 310 into the skin layer in alternating durations (durationsmarked by t₁, t₃, t_(n)) set by the frequency of the current from thepower source 108. Significantly, the active agent does not dispensepassively in the alternating instances when the polarity of the currentis opposite to the charge (i.e. attractive polarity) of the active agent(durations marked by t₂, t₄, t_(n+1)). In that instance, the oppositepolarity of the current/voltage serves as a retention mechanism of theactive agent within the electrode assembly 310.

In a double point disbursement configuration (such as described with anembodiment of FIG. 2), the alternating power source 308 alternates whichelectrode assembly is directing the active agent into the skin layer322. In one implementation, for example, both electrode assemblies maycarry the active agent, and the active agent is positively charged. At afirst duration when the current has a positive polarity, (i) apositively charged active agent in the first electrode assembly 310 isdirected into the skin layer, (ii) a positively charged active agent inthe second electrode assembly 312 is retained, or precluded from beingdiffused into the skin layer. In the next duration, when the current hasthe negative polarity, (i) a negatively charged active agent in thefirst electrode assembly 310 is retained or precluded from beingdiffused into the skin layer; and (ii) a positively charged active agentin the second electrode assembly 312 is directed into the skin layer.The timing sequence of the first electrode assembly 310 thus may bedescribed as (i) dispense at durations marked by (t₁, t₃, t_(n)), and(ii) retain at durations marked by (t₂, t₄, t_(n+1)). Likewise, timingsequence of the second electrode assembly 312 may be described as (i)dispense at durations marked (t₂, t₄, t_(n+1)) and (ii) retain atdurations marked by (t₁, t₃, t_(n)).

With regard to either the single or double point disbursementconfiguration, the frequency of the electrode assemblies operation maybe measured in milliseconds, seconds or minutes. For example, in asingle disbursement embodiment, a drug-on mode of operation may lastseveral minutes, followed by a drug-off mode. The time periods for thedrug-on and drug-off states may be the same or different. For example,the drug-on states may last several minutes, but the drug-off state maybe much shorter.

According to an embodiment, the electrode assemblies 310, 312 can beused in connection with the following mechanisms to initiate and/or stopuse of the electrode assemblies: (i) input from a user input mechanism342, (ii) input from a sensor 344 or sensor system for detecting ahuman/physiological condition, and/or (iii) a timer 346. A user inputmechanism may correspond to a switch, button or similar mechanism thatthe user can trigger. The user input mechanism 342 may be used toinitiate use of the electrode assemblies 310, 312 once the user placesthe electrode assemblies on his skin. The user input mechanism 342 mayalso be used to stop the electrode assemblies at the user's election.For example, the user may deploy the electrode assemblies on his skinlayer, then press a button or cause the power source to power theelectrodes at a desired time.

The sensor 344 (or sensor system) may correspond to a physiologicalsensor that triggers the electrode assemblies to operate when the sensor344 detects a physiological condition. For example, the sensor 344 maycorrespond to a glucose monitor for diabetics; the glucose conditionstrigger sensor 344 to actuate the electrode assemblies.

As an alternative or variation, a system such as described with FIG. 3may be provided with an interface 345 to enable the power source 308 tobe triggered or operated by the output of sensor 344 or other sensor. Inthis way, a system such as described by various embodiments may bedeployed in an environment where the user has one or more pre-existingbody sensors to detect various conditions. The interface 345 may includelogic or circuitry to enable interpretation of the sensor output fromthe user's sensor system.

The timer 346 corresponds to a mechanism, implemented by, for example,logic or circuitry, that (i) switches the power source 308 from a stateof delivery (i.e. signal current output to the electrode assemblies) toa state of non-delivery through current/voltage output; and/or (ii)switches the power source 308 from a state of non-delivery (i.e. signalreverse current or no current) to a state of delivery. In a typicalimplementation, the timer 346 may switch the power source 308 into astate in which the current output matches the charge of the active agentfor a set duration, then switch the power source to either turn off oroutput a reverse current.

As an alternative or variation to embodiments described, the sensor 344or sensor system is configured to trigger electrode assemblies 310, 312to cease operation when a physiological condition is no longer present.As still another variation, rather than switch off, an embodiment mayswitch the mode of operation of the electrode assemblies from a drugdeliver to a drug-off state. The drug-off state differs from an offstate, in that a reverse current may be used to (i) maintain theelectrodes in the deployed state, but (ii) retains the active agent withthe electrode as a result of the polarity of the current. For example,with reference to an embodiment of FIG. 1, when the sensor 344 detectspresence of the physiological condition, the electrode assembly 310switches on to deliver a type of active agent to address the condition.After the physiological condition is being detected as being treated(either by sensor or timer), the electrode assembly 310 switches into areverse current state, so that no drug is delivered into the skin layer.Subsequent re-occurrence of the condition may trigger the firstelectrode assembly 310 into the drug delivery mode again upon the sensor344 detecting re-occurrence of the physiological condition.

Various embodiments described above provide for alternatingcurrent/voltage to drive a charged active agent from an electrodeassembly into the skin layer of the user. Embodiments further recognizethat a waveform of the alternating current/voltage that is output fromthe alternating power source may be of consequence as to the operationand application for the transdermal iontophoretic delivery systemdescribed by various embodiments. Numerous current output waveforms andapplications for using such waveforms are described with FIG. 5A throughFIG. 5F.

Applications and Waveforms

FIG. 4 illustrates an alternating power source for use with embodimentssuch as described with FIG. 1 though FIG. 3. The waveform generator 400has an input to receive a DC current from a battery (or other powersource, such as photovoltaic solar cell) and converts the input into ashaped waveform. Examples of the shaped waveform may be a sinusoidalwaveform, a square waveform, a trapezoidal waveform, or other similarwaveforms. Some waveforms, such as square waves, in particular, mayshort or long frequency. Short frequency waveforms may repeat severaltimes per second (e.g. 1/60 seconds), while long frequency waveforms mayrepeat once over several minutes (e.g. 20 minute). In generating thewaveforms, some embodiments use a voltage that is in range of 1 to 100volts.

The waveform generator 400 includes power inverter 410 and waveformshaper 420. Power inverter 410 has an input to receive the DC currentand an output to transmit an AC current to the waveform shaper. Thewaveform shaper 420 includes circuitry to shape the AC current to thedesired waveform. For example, the waveform shaper 420 may includecapacitive or inductive elements in order to obtain the desired shape ofthe waveform. The shaped waveform is outputted by the waveform generator400.

FIG. 5A through FIG. 5F illustrates various waveforms or current outputvariations (over time) that can be used to promote a characteristic ofthe electrode assemblies operation on a user's skin. Embodiments such asdescribed may be implemented in either a single (see FIG. 1) or double(see FIG. 2) disbursement configuration. In describing an embodiment ofFIG. 5A-5F, reference may be made to elements or numerals of FIG. 3 forpurpose of illustration. Numerous embodiments described herein providefor waveforms that vary between a given polarity and zero, wherein atpolarity, the current causes the active agent to repel in the skinlayer. In other embodiments, the waveforms have alternative betweenpositive and negative polarity. In some embodiments, the alternatingcurrents can be delivered to each electrode assembly that is in use(whether or not the electrode assembly has the active agent). Byorienting the waveform to alternate in charged-balance fashion,electrical toxicity or damage to the skin can be reduced or minimized.In other embodiments, an alternating current is used that is orientedtowards being balanced in charge, but some asymmetry may exist.

The waveforms described below are variable between a minimum and maximumvalue. Some embodiments, such as described with FIG. 5B, may bealternating in charge value (i.e. include reverse polarity). In suchembodiments, the current delivery may be balanced in charge.

FIG. 5A illustrates a waveform 510 that includes an extended or longdrug delivery phase, according to an embodiment. In some embodiments,the skin layer may be assumed to handle only a maximum amount of currentin a given duration (max current delivery) (e.g. 80 milliamps perminute). For a given amperage, the duration of the output of thealternating power source may be set to not exceed the max currentdelivery. The delivery duration may be set to some portion or fraction(e.g. 50% for n=2) of the overall period of the current output I₁. Forexample, in some implementations, the max current delivery (I₁) isassumed to be 80 milliamps for one minute. In such an implementation,the delivery duration is set for 20 seconds on 4 milliamp output. Ratherthan switch to negative polarity, the output of the power source 308 mayalternate to no amperage output (rather than switch polarity). While thewaveform depicted in FIG. 5A is rectangular, the waveform may have analternative shape (e.g. sinusoidal, trapezoidal), with the currentdelivery corresponding to the area under the curve. In the example shownby FIG. 5A, the alternating power source 308 initiates a deliveryduration on one electrode, with delivery durations being set by acurrent that has a polarity that matches that of the charge of theactive agent. The current may alternate to zero output, in which thedrug delivery is substantially ceased. Thus, the no-delivery durationmay coincide with no current output, rather than reverse current.

FIG. 5B illustrates another embodiment in which the alternating powersignal outputs a symmetrical square wave. FIG. 5B (and other waveformsillustrated herein) illustrate use of charged balance alternatingcurrents. For example, symmetrical waveforms in polarity may beconsidered as charged balance. Depending on the application, the cyclemay be long (e.g. 20 minutes) or short ( 1/60 of a second). The deliveryduration may correspond to half of the period of the waveform. In theimplementation shown, a reverse current is used to in the non-deliveryduration, to actively prevent agent delivery to the skin layer.

FIG. 5C illustrates another embodiment in which the alternating powersignal outputs an asymmetrical square wave, in that the deliveryduration is different than the non-delivery duration. More specifically,the asymmetrical square wave may include longer delivery durations (t₁),followed by short(er) rest durations (t₂). The rest durations maycorrespond to periods of no current, or as shown, reverse current (I₂).In one application, the rest duration enable the skin layer torecuperate from the drug delivery in the prior duration (e.g., todissipate any heat, concentration of ions, or other by productsresulting from the delivery of current). As an alternative or variation,the rest period may follow a period where no current is applied to theskin layer, so as to enable the skin layer to recuperate fromapplication of current.

FIG. 5D illustrates another embodiment in which the alternating powersignal is trapezoidal, so as to include a ramp-up and/or ramp-down. Asdepicted, I₁ is the maximum current output generated from the powersource 308. The ramp-up period extends for a duration t_(r), selectedfor reasons that include enabling the user to physically accustom to theapplication of current and/or active agent. The period may be long, toenable the ramp-up duration to be effective. In an embodiment, aramp-down period may optionally be implemented.

FIG. 5E and FIG. 5F illustrate alternative waveform variations in whichhigh-frequency oscillations are superimposed on a base waveform. Thebase waveform may have a period that lasts seconds or minutes,corresponding to output current to the electrode assemblies ranging froma maximum (e.g. 4 MA) to no current and/or reverse current. Thehigh-frequency oscillations reflect small variations in the currentvalue at instances in the period. The period of the high-frequencyoscillations may be one or more magnitudes shorter than that of the basewaveform. As an example, the base waveform may have a period rangingseconds to minutes, and the high-frequency oscillations of the waveformmay have a period that ranges between milliseconds and seconds. Theeffect of the high-frequency oscillations is to reduce the effects ofthe capacitive charge in the skin layer in receiving the active agent.The high frequency oscillations may also be used to facilitate transportof the active agent through the skin including the stratum corneum bycausing oscillations in the movement of the active agent as it travelsthrough the skin so as to find pathways of least resistance throughskin. In such embodiments, the high frequency oscillations may beadjusted to enhance this effect through use of modeling (e.g.,pharmacokinetic modeling) and/or the patients age, skin type and skinlocation

The base waveform may be selected for considerations such as describedin prior embodiments. For example, in FIG. 5E, the waveform includes aramp-up time period. In FIG. 5F, the waveform has a delivery durationthat is switched to a non-delivery duration. An embodiment of FIG. 5Fillustrates that the high-frequency oscillations may be generated to bepresent only during the delivery duration.

Applications

Numerous applications exist for embodiments described herein. Table 1lists, for example, various medical conditions that may be treated withvarious drugs and other active agents, using a system of electrodeassemblies such as described above. The table further identifies whetherthe treatment can be patient activated, sensor activated, timed, orcontinuous. If patient activated, a user input mechanism 342 (FIG. 3)may be operated by the user when the electrode assemblies are in thedeployed state to initiate operation of the electrode assemblies (anddelivery of the active agent). Examples of user activated applicationsinclude delivery of various pain management drugs such as lidocaine orfentanyl. Sensor activated uses may incorporate use of one or moresensors 344 that interface with the user's body to determine whether acondition of the user requires treatment with the identified activeagent. An example of a sensor activated application can includetreatment of diabetes where the sensor is a blood glucose sensor or(other sensor means for detecting hyperglycemia) and administers a doseof insulin. A treatment is timed if it incorporates the timer 346 todetermine when to start/stop the delivery durations.

TABLE 1 Patient Sensor Contin- Active Agent Condition ActivatedActivated Timed uous Insulin Diabetes X X X GLP-1/ Diabetes X X XIntegrin Fe²⁺ Anemia X Sodium Electrolyte X (Na), Potassium renewal (K)Furosemide Epilepsy X X Bumetanide Migraine X X X Aspirin Inflammation XX X Ketoprophin Arthritis X Lidocaine Pain X Fentanyl Pain X AlprazolinAnxiety/Pain X X Antibiotics Wound X Healing

In specific embodiments, the active agent can comprise a sufficientamount of elemental iron for the treatment of iron deficiency anemia.The amount of elemental iron can be sufficient to provide between 1 to100 mg of elemental iron to the patient for a period of days or evenweeks. In various embodiments the elemental iron can comprise ionic ironin the form of ferrous (Fe²⁺) or ferric (Fe³⁺) iron. The ionic iron cancomprise an iron salt, a ferrous salt, a ferric salt, ferricpyrophosphate ferrous chloride or a combination thereof.

Although illustrative embodiments of the invention have been describedin detail herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments. As such, many modifications and variations will be apparentto practitioners skilled in this art. Accordingly, it is intended thatthe scope of the invention be defined by the following claims and theirequivalents. Furthermore, it is contemplated that a particular featuredescribed either individually or as part of an embodiment can becombined with other individually described features, or parts of otherembodiments, even if the other features and embodiments make nomentioned of the particular feature. This, the absence of describingcombinations should not preclude the inventor from claiming rights tosuch combinations.

What is claimed is:
 1. A system for transdermal delivery of activeagents for therapeutic and medicinal purposes, the system comprising: apower source that provides a charged balanced alternating output currentthat varies between a first current value and a second current value; apair of electrode assemblies, each electrode assembly being configuredto be held in contact with a skin layer of a user, and wherein eachelectrode assembly includes an electrode that is coupled to the powersource to receive the output current; wherein at least one of theelectrode assemblies in the pair includes a medium that carries anactive agent having a charge, the medium being provided on the at leastone electrode assembly to enable the output current to repel the activeagent into the skin layer for a duration in which the output current hasa polarity that is the same as a polarity of the active agent.